Police in Belarus have arrested two people accused of organising the bombing in a Minsk metro station on Monday, which killed 12 commuters and injured up to 150.

President Alexander Lukashenko said the suspects were held on Tuesday in what he described as a "brilliant operation" by police and the KGB. "The main thing is that we know who carried out this attack, and how," he said. "It's not clear yet why, but that will soon become known."

No details of the alleged attackers were given, but identikit photographs of two suspects showed a fair-haired Slavic-looking man and another with darker features wearing a woollen hat. Both appeared to be under 30.

The bomb, placed under a bench on the platform at Oktyabrskaya station in the centre of the capital, exploded just before 6pm on Monday. Bloodied survivors staggered outside as thick smoke filled the metro.

Security sources told news agencies that surveillance cameras recorded a man putting a bag under the bench, ascending the escalator and then reaching under his coat to detonate the explosives. The man was identified in earlier footage, in which he regularly left the metro at a different station.

Officers who staked out the station exit identified the man and followed him to his home, where he was arrested by police special forces.

Lukashenko said the detainees admitted the attack and two other bombings, one in the city of Vitebsk in 2005 and another in a Minsk park in 2008, both of which injured about 50 people.

Lukashenko, an autocrat who has been in office since 1994, signalled that Belarus's beleaguered liberal opposition could be made a scapegoat for the attack when he said "the fifth column" should be questioned.

"Bring in everyone and interrogate them, pay no attention to democracy or the groans and howls of the foreign martyrs," he ordered security bosses. "We must not relax our efforts. The mop-up operation must be total."